JP2016173212A - Water heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water heater which can suppress generation of hunting even when a gap occurs between an output which can be dealt with at one combustion stage and an output which can be dealt with at the other combustion stage.SOLUTION: In the case where an unadjustable range, which is a numerical range surpassing an upper limit value and below a lower limit value, has occurred between an upper limit value of a combustion output in an i-th combustion stage and a lower limit value of the combustion output in an i+1-th combustion stage, a controller which a water heater has determines that such an unadjustable range has occurred (S310, S340). In the case where a necessary combustion output is in the unadjustable range, a switching valve, a proportional control valve and a blower are controlled so that an actual combustion output is fixed at one of the upper limit value of the combustion output in the i-th combustion stage, and the lower limit value of the combustion output in the i+1-th combustion stage (S340: YES).SELECTED DRAWING: Figure 7

Description

  The present invention relates to a water heater.

  There is known a water heater configured such that a plurality of combustion stages whose ranges from a lower limit value to an upper limit value of the combustion output are different from each other can be switched to any one (see, for example, Patent Document 1). Patent Document 1 below also describes that hunting may occur in switching of the combustion stage.

JP 2013-245892 A

  By the way, when nozzle clogging occurs due to aging deterioration of the water heater, etc., even if the fan speed is adjusted properly and the opening of the gas proportional control valve is adjusted properly, Input may not be obtained. Further, even when the gas supply pressure is significantly reduced due to a factor on the supply source side that supplies gas to the water heater, the desired input may not be obtained as described above.

  In such a case, there is a gap between the upper limit value of the output that can be handled by the first combustion stage and the lower limit value of the output that can be handled by the second combustion stage that is one level higher. May occur. If you try to adjust the hot water temperature by feedback control so that the temperature difference becomes small based on the temperature difference between the set temperature and the hot water temperature without recognizing on the water heater side that such a gap has occurred, Hunting may occur during stage switching.

  More specifically, in the feedback control, when the output that is originally required is within the above-described gap, even if the output is increased to the upper limit in the first combustion stage, the tapping temperature is higher than the expected temperature. Since the temperature is also low, switching to the second combustion stage is performed. However, when switching to the second combustion stage, even if the output is lowered to the lower limit value in the second combustion stage, the tapping temperature will be higher than the expected temperature. Switching to is performed. Therefore, if this situation is repeated, hunting occurs in switching the combustion stage.

  Due to the above circumstances, a water heater that can suppress the occurrence of hunting even when a gap is generated between an output that can be handled by one combustion stage and an output that can be handled by the other combustion stage. It is desirable to provide

  The water heater described below supplies a plurality of burners, a proportional control valve capable of adjusting the fuel supply amount to the burner, a blower capable of adjusting the air supply amount to the burner, and a fuel to each of the plurality of burner portions. A switching valve capable of switching whether or not to perform and a switching valve to control which of the plurality of burner sections supplies fuel, thereby allowing a plurality of combustion output lower and upper limit values to be different from each other. A control unit capable of switching the combustion stage to any one and adjusting the combustion output within the range from the lower limit value to the upper limit value of the combustion output in each combustion stage by controlling the proportional control valve and the blower, The control unit calculates a necessary combustion output necessary for tapping at the set temperature based on the arbitrarily set temperature and the actual tapping temperature, so that the necessary combustion output is obtained, Example: The feedback control unit that controls the control valve and the blower, and the 1st to nth combustion stages (where n is an integer of 2 or more) in which the combustion output sequentially increases, i-th (where i is 1) ≦ i <n is an integer that satisfies the upper limit value of the combustion output in the combustion stage and the lower limit value of the combustion output in the (i + 1) th combustion stage, and is a numerical range that is above the lower limit value and lower than the lower limit value. When the required combustion output calculated by the determination unit capable of determining that the non-adjustable range has occurred and the feedback control unit is within the non-adjustable range determined by the determination unit, the actual combustion output is i Feedback control for controlling the switching valve, the proportional control valve and the blower so as to be fixed at either the upper limit value of the combustion output in the first combustion stage or the lower limit value of the combustion output in the i + 1th combustion stage And a locking portion.

  According to the water heater configured as described above, the feedback control unit calculates the necessary combustion output necessary for the hot water at the set temperature based on the arbitrarily set temperature and the actual hot water temperature, and The switching valve, the proportional control valve, and the blower are controlled so that the combustion output is obtained. At that time, the determination unit includes an upper limit value of the combustion output in the i-th combustion stage and a lower limit value of the combustion output in the i + 1th combustion stage among the first to n-th combustion stages in which the combustion output sequentially increases. In the meantime, it is determined whether or not an unadjustable range that is a numerical range that exceeds the upper limit value and falls below the lower limit value occurs. When the necessary combustion output calculated by the feedback control unit is within the non-adjustable range determined by the determination unit, the feedback control prohibiting unit determines that the actual combustion output is the upper limit value of the combustion output in the i-th combustion stage, Alternatively, the switching valve, the proportional control valve, and the blower are controlled so as to be fixed at any one of the lower limit values of the combustion output in the (i + 1) th combustion stage. Therefore, unlike the case where the combustion stage is switched by the feedback control unit without recognizing that the non-adjustable range has occurred, the occurrence of hunting in the switching of the combustion stage can be suppressed.

FIG. 1 is a configuration diagram of a water heater. FIG. 2A is an explanatory diagram showing standard characteristics of a plurality of combustion stages. FIG. 2B is an explanatory diagram showing characteristics when a gap is generated between the combustion stages. FIG. 3 is an explanatory diagram for explaining the transition of the operating state of the water heater. FIG. 4 is a flowchart showing hot water supply processing in the first embodiment. FIG. 5 is a flowchart showing feedback temperature control in the first embodiment. FIG. 6 is a flowchart showing output increase control in the first embodiment. FIG. 7 is a flowchart showing output increase control in the first embodiment. FIG. 8 is a flowchart showing hot water supply processing in the second embodiment. FIG. 9 is a flowchart showing feedback temperature control in the second embodiment. FIG. 10 is a flowchart showing output increase control in the second embodiment. FIG. 11 is a flowchart showing output increase control in the second embodiment.

Next, the above-described water heater will be described with reference to an exemplary embodiment.
(1) First embodiment [Structure of water heater]
As shown in FIG. 1, the water heater 1 is configured to be able to supply hot water to a hot water outlet such as a hot water tap 2. The water heater 1 has a combustion chamber 11, and burners 12A, 12B, and 12C, a primary heat exchanger 13, a secondary heat exchanger 14, an electrode 15, an igniter 16, and a frame rod 17 are included in the combustion chamber 11. Is arranged.

  The primary heat exchanger 13 is a heat exchanger that mainly recovers sensible heat from the high-temperature exhaust gas generated by combustion in the burners 12A, 12B, and 12C. The secondary heat exchanger 14 is a primary heat exchanger. This is a heat exchanger that mainly recovers latent heat from the exhaust gas whose temperature has decreased due to heat exchange in the vessel 13.

  In the secondary heat exchanger 14, in order to further take heat from the exhaust having a relatively high relative humidity, water vapor in the exhaust is condensed and drain (condensed water) is generated. Therefore, a drain drain pipe 18 is provided to discharge this drain, and a neutralizer 19 is provided at the downstream end of the drain drain pipe 18. The neutralizer 19 is provided to neutralize acidic drain containing nitrogen oxides or sulfur oxides. A neutralizer (for example, neutralizing drain) is provided inside the neutralizer 19. , Calcium carbonate).

  The water heater 1 includes a fan motor 20 and a fan 21, and is configured to be able to supply air into the combustion chamber 11 by rotationally driving the fan 21 by the fan motor 20. An exhaust top 22 is provided in the upper part of the combustion chamber 11, and the exhaust can be exhausted outside the combustion chamber 11 through the exhaust top 22. Further, the combustion chamber 11 is provided with an overheat prevention device 23 that forcibly stops the operation of the water heater 1 by fusing when the surroundings are in an abnormally high temperature state.

  Moreover, the water heater 1 includes a gas supply pipe 31 that serves as a gas supply path to the burners 12A, 12B, and 12C. The gas supply pipe 31 includes a main pipe 32 whose upstream end is connected to a gas supply source (for example, a city gas pipe or a propane gas pipe), and branch pipes 33A, 33B, and 33C branched from the main pipe 32 into a plurality. It consists of and. Nozzles 34A, 34B, and 34C are provided at the downstream ends of the branch pipes 33A, 33B, and 33C, and gas can be supplied to the burners 12A, 12B, and 12C via the nozzles 34A, 34B, and 34C.

  In the gas supply pipe 31, the main pipe 32 is provided with an original electromagnetic valve 35 and a gas proportional control valve 36. The branch pipes 33A, 33B, and 33C are provided with switching electromagnetic valves 37A, 37B, and 37C.

  Further, the water heater 1 includes a water supply pipe 41 that forms a water inlet to the secondary heat exchanger 14, a hot water pipe 43 that forms a water outlet from the primary heat exchanger 13, and a water supply pipe 41. A bypass pipe 45 branched from the middle of the flow path and communicating with the hot water discharge pipe 43 is provided.

  Among these water pipes, the water supply pipe 41 is connected to a water supply source (for example, a water pipe) on the upstream end side, and is located in the middle of the flow path from the upstream end side to the downstream end side of the water supply pipe 41. , A strainer 51 for filtering water flowing from the upstream side to the downstream side in order from the upstream end side, a water amount sensor 52 for detecting the amount of water flowing in the water supply pipe 41, and a water amount control motor for increasing / decreasing the amount of water flowing in the water supply pipe 41 53 and a thermistor 54 for detecting the incoming water temperature for detecting the temperature of the water flowing to the primary heat exchanger 13 are provided. In addition, a freeze prevention heater 55 is provided in the middle of the water inlet.

  The hot water discharge pipe 43 has a downstream end connected to a hot water outlet (a place where the hot water tap 2 is present in the present embodiment), and an upstream end in the middle of the flow path from the upstream end to the downstream end of the hot water discharge pipe 43. In order from the side, the temperature of the hot water is detected on the downstream side of the junction of the hot water outlet pipe 43 and the bypass pipe 45, the thermistor 56 for detecting the temperature of the hot water flowing out from the primary heat exchanger 13 A hot water temperature detection thermistor 57, a water drain plug 58 with a pressure relief valve, and the like are provided. The bypass pipe 45 is provided with a bypass control motor 59 that performs increase / decrease control of the amount of water flowing through the bypass pipe 45.

  In addition, the water heater 1 includes a controller 61 and a remote controller 62. The controller 61 incorporates a microcomputer having a CPU, ROM, RAM, and the like. The various sensors described above (the frame rod 17, the water temperature detecting thermistor 54, the inner trunk outlet hot water temperature detecting thermistor 56, and Information is input from the hot water temperature detection thermistor 57, etc., and the above-described various solenoid valves (original solenoid valve 35, gas proportional control valve 36, switching solenoid valves 37A, 37B, 37C, etc.), various motors (fan motor 20). The water amount control motor 53, the bypass control motor 59), the igniter 16 and the like are controlled.

  The remote controller 62 includes a user interface such as an input unit that receives an input operation from the user and an output unit that displays information and outputs audio to the user. Information input from the input unit is transmitted to the controller 61. Based on the information transmitted from the controller 61, information is displayed and audio is output from the output unit.

[Operation mode during hot water supply]
In the water heater 1 configured as described above, when the user opens the hot-water tap 2, the water flowing in from the water inlet passes through the water amount sensor 52 and the secondary heat exchanger 14 to the primary heat exchanger 13. Head. At this time, the water amount sensor 52 outputs a signal having a frequency corresponding to the flow velocity. When the controller 61 senses that this signal has reached the specified frequency, the controller 61 controls the fan motor 20 to rotate the fan 21. Let

  After the fan 21 rotates and the pre-purge operation is performed, the igniter 16 operates and discharges from the electrode 15. Subsequently, the original solenoid valve 35 and the switching solenoid valves 37A to 37C are opened, and the gas proportional control valve 36 performs a slow ignition operation to ignite the burners 12A to 12C. After ignition, the flame is detected by the frame rod 17, and when it is confirmed that the flame is burning, the slow ignition operation is terminated.

  When the slow ignition operation is finished, the proportional control is subsequently started. If there is a difference between the hot water temperature detected by the hot water temperature detection thermistor 57 and the set temperature arbitrarily set by the user, the controller 61 determines that there is a difference, and the gas proportional control valve 36 and the switching electromagnetic valve 37A. By opening and closing at 37C, the amount of gas is continuously changed to keep the hot water temperature constant. In addition, since the water amount control motor 53 adjusts the water amount to an appropriate amount, the maximum amount of hot water is always secured. At this time, a signal is sent from the controller 61 to the fan motor 20 in accordance with a change in the gas amount by the gas proportional control valve 36, whereby the relationship between the gas amount and the air amount is always maintained in a predetermined relationship. .

  When the user closes the hot-water tap 2 in the situation where the hot water supply is performed as described above, the frequency signal from the water amount sensor 52 disappears, so the controller 61 controls the original solenoid valve 35 and the switching solenoid valves 37A to 37C. Is closed, the fire is extinguished, and a post-purge operation is started. Thereafter, when the post-purge operation times out, the fan 21 stops.

  At the time of hot water supply, based on the incoming water temperature detected by the incoming water temperature detection thermistor 54, the set temperature arbitrarily set by the user by operating the remote controller 62, and the flow rate detected by the water amount sensor 52, the set temperature The combustion output (hereinafter also referred to as output) required for the hot water is calculated. Then, feedforward control (hereinafter referred to as FF control) is performed according to the required output, the combustion stage corresponding to the required output is set, the rotational speed of the fan 21 and the gas proportional control. The opening degree of the valve 36 is set.

  The above-described combustion stage is switched depending on which one of the switching electromagnetic valves 37A to 37C is opened and which is closed, and in this embodiment, the combustion stage can be switched to four stages. In the combustion stage having four stages, the numerical range of output that can be handled in each stage is different as shown in FIG. The output at each combustion stage is determined according to the rotational speed of the fan 21 and the opening of the gas proportional control valve 36. In FIG. 2A, the correspondence relationship between the output at each combustion stage and the rotation speed of the fan 21 is graphed.

  In the design of the water heater 1, the output upper limit value in the i-th combustion stage (where i is an integer satisfying 1 ≦ i <n. In this embodiment, n = 4) is the i + 1th combustion stage. It is comprised so that it may become larger than the lower limit of the combustion output in. Therefore, the numerical range of output that can be handled in the i-th combustion stage and the numerical range of output that can be handled in the (i + 1) -th combustion stage are numerical ranges that overlap each other (in FIG. 2A). (See the range indicated by double-ended arrows.)

  After the combustion stage corresponding to the required output is set by the FF control and the rotation speed of the fan 21 and the opening of the gas proportional control valve 36 are set, the temperature difference between the set temperature and the tapping temperature is further increased. Based on this, feedback control (hereinafter referred to as FB control) is performed. That is, based on the temperature difference between the set temperature and the tapping temperature, the rotation speed of the fan 21 and the opening of the gas proportional control valve 36 are adjusted so that this temperature difference is reduced.

[Causes and problems of non-adjustable range]
By the way, when nozzle clogging or the like occurs in the nozzles 34A, 34B, 34C due to aging deterioration of the water heater 1, etc., the rotational speed of the fan 21 is adjusted appropriately and the opening degree of the gas proportional control valve 36 is adjusted. Even if the value is adjusted appropriately, the desired input may not be obtained. Further, even when the gas supply pressure is remarkably reduced due to a factor on the supply source side that supplies gas to the water heater 1, the rotational speed of the fan 21 is appropriately adjusted and the gas proportional control valve 36 is Even if the opening is adjusted appropriately, the desired input may not be obtained. As a result, the output (combustion output) determined by the product of thermal efficiency and input falls into a state where the desired output cannot be obtained. Depending on the situation at this time, the output characteristics of each combustion stage may change from the standard output characteristics shown in FIG. 2A to the output characteristics shown in FIG. 2B, for example.

  Even when the output characteristics as shown in FIG. 2 (B) are obtained, the rotation speed of the fan 21 is low and the opening of the gas proportional control valve 36 is small (the graph of each combustion stage shown in FIG. 2 (A)). In the region near the left end in the above), the influence of nozzle clogging is relatively small. Therefore, the output characteristics of each combustion stage are almost the same as the standard output characteristics shown in FIG. On the other hand, in a region where the rotational speed of the fan 21 is high and the opening degree of the gas proportional control valve 36 is large (region near the right end in the graph of each combustion stage shown in FIG. 2A), nozzle clogging or the like. The effect appears relatively large. Therefore, the output characteristics of each combustion stage (see the graph shown by the solid line in FIG. 2B) are different from the standard output characteristics (see the graph shown by the broken line in FIG. 2B). Even if the rotational speed of the fan 21 is increased and the opening degree of the gas proportional control valve 36 is increased, the output does not increase as expected.

  In such a situation, as shown in FIG. 2B, between the numerical range of the output that can be handled by the i-th combustion stage and the numerical range of the output that can be handled by the i + 1-th combustion stage. There is a case where there is no overlapping range, and a gap (see a hatched range in FIG. 2B) may occur between both numerical ranges. This gap allows the rotational speed of the fan 21 and the opening of the gas proportional control valve 36 to be adjusted so that the output within the gap can be obtained regardless of whether the combustion stage is switched to the i-th or the (i + 1) th combustion stage. This is a range that cannot be adjusted (hereinafter referred to as an unadjustable range).

  When the output calculated in the above-described FF control becomes a value included in the above-described non-adjustable range, the following problems occur when the above-described FB control is performed.

  As illustrated in FIG. 3, when the output necessary for the FF control is calculated, the rotation speed of the fan 21 and the opening of the gas proportional control valve 36 corresponding to the output are determined. Trying to act on a point. However, since the point A is actually included in the non-adjustable range, the water heater 1 operates at the point B even if the rotational speed of the fan 21 and the opening of the gas proportional control valve 36 are adjusted as designed. To do. In this case, the water heater 1 is in a state where only an output smaller than the point A can be obtained.

  Therefore, since the hot water temperature at this time becomes lower than the set temperature, when the FB control is performed based on the temperature difference between the set temperature and the hot water temperature, the hot water heater 1 changes the operating state from the A point to the C point side. Try to fluctuate. That is, the water heater 1 tries to raise the hot water temperature by the FB control. However, since the water heater 1 is actually operated at the point B, when the FB control is performed, the operating state of the water heater 1 changes from the B point to the D point side.

  Therefore, even if the operating state of the water heater 1 gradually changes from the B point to the D point by the FB control, a state in which only an output smaller than the A point is obtained at the maximum continues during that time. When the operating state of the water heater 1 reaches the point D, the water heater 1 recognizes that the operating state has reached the point C. Therefore, in the FB control, in order to further increase the output, Perform stage switching. Thereby, the water heater 1 shifts to a state of operating at the point E. The hot water heater 1 intends to move the operating state from the point C to the point E, but actually, the operating state shifts from the point D to the point E.

  When the operating state of the water heater 1 shifts to the point E, the water heater 1 enters a state where an output larger than the point A can be obtained. Therefore, in this state, the hot water temperature becomes higher than the set temperature, so that the water heater 1 changes the operating state from the E point to the F point side by the FB control. That is, the water heater 1 tries to lower the hot water temperature by the FB control. And even if the operating state of the water heater 1 fluctuates to the point F, the water heater 1 is still in a state where an output larger than the point A can be obtained. Therefore, in the FB control, the combustion stage is switched in order to further reduce the output.

  At the time of this switching, the water heater 1 tries to shift to a state where it operates at point G. However, even if the rotation speed of the fan 21 and the opening degree of the gas proportional control valve 36 are adjusted as designed so as to operate at the point G, the water heater 1 is operated at the point H. In this case, the water heater 1 is in a state where only an output smaller than the point A can be obtained.

  Therefore, since the hot water temperature at this time is lower than the set temperature, when the FB control is performed, the water heater 1 tries to change the operating state from the G point to the C point side. The operating state of 1 changes from the H point to the D point side. That is, the water heater 1 tries to raise the hot water temperature again by the FB control.

  When the FB control as described above is performed, when the combustion stage is switched in order to increase the tapping temperature, the tapping temperature becomes too high, and when the combustion stage is switched to decrease the tapping temperature, the tapping temperature becomes too low. , Fall into the situation. Therefore, the hunting state in which the switching of the combustion stage is repeated without obtaining the desired hot water temperature indefinitely will occur. Therefore, in the water heater 1 of the present embodiment, the hot water supply process described below is executed in order to suppress the occurrence of hunting even when the above-described non-adjustable range occurs. .

[Hot water treatment]
Hereinafter, the hot water supply process performed in the hot water heater 1 of the present embodiment will be described with reference to FIGS. This hot water supply process is a process that is always executed in the controller 61 when the water heater 1 is in an operating state.

  When the hot water supply process is started, the controller 61 first determines whether or not the flow rate detected by the water amount sensor 52 is equal to or greater than a predetermined threshold value (S10), and when the flow rate is less than the predetermined threshold value. (S10: NO), S10 is repeated by returning to S10.

  On the other hand, when the flow rate is equal to or higher than the predetermined threshold value in S10 (S10: YES), the controller 61 detects the incoming water temperature detected by the incoming water temperature detection thermistor 54, the set temperature set in the remote controller 62, and The necessary output is calculated based on the flow rate detected by the water amount sensor 52 (S15). Then, the controller 61 sets the combustion stage according to the required output calculated in S15, and the rotational speed of the fan 21 and the gas proportional control valve so that the required output can be obtained at the combustion stage. An opening of 36 is set (S20).

  Subsequently, the controller 61 starts combustion in the burners 12A to 12C (S25). In the ignition sequence of S25, the fan motor 20 is first driven, and the fan 21 is rotated at the rotation speed set in S20 to start blowing air, and the opening degree of the gas proportional control valve 36 is set in S20. Adjust to the desired opening. Subsequently, the igniter 16 is actuated to start discharging by the electrode 15, and the switching electromagnetic valves 37A to 37C corresponding to the combustion stage set in S20 are opened. Thereby, gas is supplied to the nozzles 34A to 34C corresponding to the combustion stage set in S20, and combustion is started in the burners 12A to 12C corresponding to the combustion stage set in S20. The

  Subsequently, the controller 61 determines whether or not the flow rate detected by the water amount sensor 52 is equal to or less than a predetermined threshold value (S30). If the flow rate exceeds a predetermined threshold value (S30: NO), it is determined whether there has been a change in the incoming water temperature, the set temperature, or the flow rate (S35). When it is determined in S35 that there is no change in the incoming water temperature, the set temperature, or the flow rate (S35: NO), the controller 61 waits for a predetermined time until the hot water temperature becomes stable (S40), and executes feedback temperature control. (S45). Details of the feedback temperature control in S45 will be described later. When S45 is finished, the process returns to S30. Thereby, when the flow rate exceeds a predetermined threshold and there is no change in the incoming water temperature, the set temperature, or the flow rate (S30: NO, S35: NO), S30 to S45 are repeatedly executed. become.

  On the other hand, when S30 to S45 are repeatedly executed and the incoming water temperature, the set temperature, or the flow rate is changed, an affirmative determination is made in S35 (S35: YES). In this case, the controller 61 turns off the flag F1 (S50). The flag F1 is a flag that can be switched on and off during the execution of the feedback temperature control of S45, and details thereof will be described later.

  Subsequently, the controller 61 calculates a required output based on the incoming water temperature, the set temperature, and the flow rate (S55). Then, the combustion stage is set according to the required output, and the rotation speed of the fan 21 and the opening of the gas proportional control valve 36 are set so that the required output can be obtained at the combustion stage (S60). ). That is, in response to the change in the incoming water temperature, the set temperature, or the flow rate, in S55 to S60, settings equivalent to S15 to S20 are performed again. When S60 ends, the process returns to S30. As a result, when the flow rate exceeds a predetermined threshold value and there is no change in the incoming water temperature, the set temperature, or the flow rate (S30: NO, S35: NO), S30 to S45 are repeated. It will be.

  In addition, when S30 to S45 are repeatedly executed and the flow rate becomes equal to or lower than the predetermined threshold (S30: NO), an affirmative determination is made in S30 (S30: YES). In this case, the controller 61 stops the combustion in the burners 12A to 12C (S65), and returns to S10. In S65, all the switching solenoid valves 37A to 37C are closed. Further, the fan motor 20 is stopped for a predetermined time for exhaust and heat dissipation, and then the fan motor 20 is stopped.

  Next, the feedback temperature control in S45 will be described. When the feedback temperature control is started, the controller 61 first determines whether or not the tapping temperature is lower than the set temperature as shown in FIG. 5 (S110). When it is determined in S110 that the tapping temperature is lower than the set temperature (S110: YES), the controller 61 performs output increase control to increase the tapping temperature (S120). The output increase control in S120 is a process as shown in FIG.

  When the output increase control is started, as shown in FIG. 6, the controller 61 determines whether or not the maximum output of the current combustion stage has been reached (S210). In S210, a negative determination is made when there is room to further increase the output only by adjusting the rotation speed of the fan 21 and the opening of the gas proportional control valve 36 while maintaining the current combustion stage (S210). : NO). In this case, the controller 61 adjusts the rotation speed of the fan 21 so as to increase the output, adjusts the opening of the gas proportional control valve 36 (S220), and ends the output increase control.

  On the other hand, in S210, if the output of the fan 21 and the opening of the gas proportional control valve 36 are adjusted with the current combustion stage alone, the output cannot be further increased. (S210: YES). In this case, the controller 61 turns on the flag F1 (S260) and stores that the combustion stage is increased by one stage. Then, the controller 61 changes the combustion stage from the N stage to the N + 1 stage (S270). In S270, if the current combustion stage is 1 stage, it is changed to 2 stages, if the current combustion stage is 2 stages, it is changed to 3 stages, and if the current combustion stage is 3 stages, it is changed to 4 stages.

  Although illustration is omitted, even if an affirmative determination is made in S210, if the current combustion stage is four stages, the combustion stage cannot be further increased. Therefore, in that case, the current output may be maintained by ending the output increase control without executing S260, S270, and S220.

  When S270 is completed, the process proceeds to S220 described above. Thereby, the rotation speed of the fan 21 and the opening degree of the gas proportional control valve 36 are adjusted so that the output increases in the combustion stage raised by one stage in S270 (S220). When S220 is finished, the output increase control is finished.

When the output increase control is finished as described above, S120 in FIG. 5 is finished. In this case, the feedback temperature control shown in FIG. 5 is finished.
If it is determined in S110 shown in FIG. 5 that the tapping temperature is equal to or higher than the set temperature (S110: NO), the controller 61 determines whether the tapping temperature is higher than the set temperature (S130). When it is determined in S130 that the tapping temperature is higher than the set temperature (S130: YES), output reduction control is executed to lower the tapping temperature (S140). The output reduction control in S140 is a process as shown in FIG.

  When the output reduction control is started, the controller 61 determines whether or not the minimum output of the current combustion stage has been reached as shown in FIG. 7 (S310). In S310, a negative determination is made when there is room to further reduce the output only by adjusting the rotation speed of the fan 21 and the opening of the gas proportional control valve 36 while maintaining the current combustion stage (S310). : NO). In this case, the controller 61 adjusts the rotation speed of the fan 21 so as to reduce the output, adjusts the opening degree of the gas proportional control valve 36 (S320), and ends the output reduction control.

  On the other hand, in S310, if the output of the fan 21 and the opening of the gas proportional control valve 36 are adjusted with the current combustion stage alone, the output cannot be further reduced. (S310: YES). In this case, the controller 61 determines whether or not the flag F1 is on (S340).

  In S340, when the flag F1 is OFF (S340: NO), it is understood that S260 to S270 are not executed in the output increase control. Therefore, in this case, the controller 61 changes the combustion stage from the N stage to the N-1 stage (S370). In S370, if the current combustion stage is four stages, it is changed to three stages, if the current combustion stage is three stages, it is changed to two stages, and if the current combustion stage is two stages, it is changed to one stage.

  Although illustration is omitted, even if an affirmative determination is made in S310, if the current combustion stage is one stage, the combustion stage cannot be lowered any further. Therefore, in that case, the current output may be maintained by terminating the output reduction control without executing S340, S370, and S320.

  When S370 is finished, the process proceeds to S320 described above. Thereby, the rotation speed of the fan 21 and the opening degree of the gas proportional control valve 36 are adjusted so that the output decreases in the combustion stage lowered by one stage in S370 (S320). When S320 is finished, the output reduction control is finished.

  In S340, when the flag F1 is ON (S340: YES), it is understood that S260 to S270 are executed in the output increase control. In this case, although S270 is executed and the combustion stage is increased by one stage, it is necessary to lower the combustion stage by one stage at the present stage. Therefore, from this fact, the controller 61 recognizes that the non-adjustable range as described above has occurred, and in this case, the output reduction control is terminated without executing S370 and S320. Maintain the output of.

When the output reduction control is finished as described above, S140 in FIG. 5 is finished. In this case, the feedback temperature control shown in FIG. 5 is finished.
In S130 shown in FIG. 5, if the tapping temperature is determined to be equal to or lower than the set temperature (S130: NO), it means that the tapping temperature matches the set temperature. In that case, the flag F1 is turned off. (S150), and the feedback temperature control shown in FIG. Note that “the temperature of the tapping water is equal to the set temperature” means that the temperature difference between the two is within a predetermined error range (for example, within ± 1 ° C.). It does not mean that the difference is completely zero.

  When the hot water supply process as described above is executed, the hot water heater 1 tries to operate at the point A shown in FIG. When the water heater 1 is operated at the point B, the output becomes too small, so S120 in FIG. 5 (specifically, output increase control shown in FIG. 6) is executed. As a result, the water heater 1 tries to change the operating state from the A point to the C point side, but actually, the operating state of the water heater 1 changes from the B point to the D point side.

  Thereafter, when the operating state reaches the point D, the water heater 1 recognizes that the operating state has reached the point C, so an affirmative determination is made in S210 of FIG. 6, and the flag F1 is set in S260. Turned on, the combustion stage is raised by one stage in S270. Thereby, the water heater 1 shifts to a state of operating at the point E.

  When the operating state of the water heater 1 shifts to the point E, the water heater 1 enters a state where an output larger than the point A can be obtained. For this reason, the output becomes excessive, and in this state, the tapping temperature becomes higher than the set temperature, so S140 in FIG. 5 (specifically, output reduction control shown in FIG. 7) is executed. Thereby, the operating state of the water heater 1 changes from the E point to the F point side.

  Thereafter, even when the operating state of the water heater 1 reaches the point F, the water heater 1 is still in a state where an output larger than the point A can be obtained. Therefore, an affirmative determination is made in S310 of FIG. However, at this time, since the flag F1 is turned on in the previously executed S260, the water heater 1 recognizes that the non-adjustable range as described above has occurred, and an affirmative determination is made in S340. Thereby, the switching of the combustion stage (S370) is not performed. As a result, the water heater 1 continues to operate at point F. That is, when the water heater 1 recognizes that the non-adjustable range is generated, the water heater 1 continues to operate at the point F, and thereby suppresses occurrence of hunting in switching of the combustion stage.

  Note that when the operating state of the water heater 1 shifts from the point D to the point E, there is a possibility that the hot water temperature and the set temperature may transiently coincide with each other. The flag F1 may be configured to be turned off when the tapping temperature and the set temperature are in a state that coincides with a period sufficiently longer than the period assumed to be the target.

  In the first embodiment described above, the controller 61 functions as a feedback control unit referred to in this specification by executing the feedback temperature control shown in FIG. Further, the controller 61 executes S210 and S260 in FIG. 6 and S310 and S340 in FIG. 7 to function as a determination unit in this specification. Furthermore, when the controller 61 makes an affirmative determination in S310 of FIG. 7 and skips S370 and S320, the controller 61 functions as a feedback control prohibition unit in this specification.

(2) Second Embodiment Next, a second embodiment will be described. In addition, since 2nd embodiment only changed a part of hot water supply process illustrated by 1st embodiment, it describes in full detail centering on difference with 1st embodiment, and regarding the part similar to 1st embodiment. Will not be described in detail.

[Hot water treatment]
Hereinafter, the hot water supply process performed in the water heater 1 of this embodiment is demonstrated based on FIGS. The processes shown in FIGS. 8 to 11 correspond to the processes shown in FIGS. 4 to 7, and the same processing steps in the corresponding processes are denoted by the same reference numerals.

  The difference between the hot water supply process shown in FIG. 8 and the hot water supply process shown in FIG. 4 is that the flag F1 is turned off in S50 in the hot water supply process shown in FIG. 4, whereas in the hot water supply process shown in FIG. Is that the flags F1 and F2 are turned off. As will be described in detail later, the flag F1 is a flag that is turned on when the combustion stage is switched in the output increase control shown in FIG. 10, and this is the same as in the first embodiment. On the other hand, the flag F2 is a flag that is turned on when the combustion stage is switched in the output reduction control shown in FIG. 11, and this is a configuration that is not in the first embodiment.

  The difference between the feedback temperature control shown in FIG. 9 and the feedback temperature control shown in FIG. 5 is that in the feedback temperature control shown in FIG. 5, the flag F1 was turned off in S150, whereas in the feedback temperature control shown in FIG. The flag F1 and F2 are turned off in S151 instead of S150.

  The difference between the output increase control shown in FIG. 10 and the output increase control shown in FIG. 6 is that processing steps S230, S240, and S250 that are not included in the output increase control shown in FIG. 6 are added. .

Hereinafter, the output increase control in the present embodiment will be described focusing on the above differences. When the output increase control is started, as shown in FIG. 10, the controller 61 determines whether or not the maximum output of the current combustion stage has been reached (S210). In S210, as in the first embodiment, when the rotation speed of the fan 21 and the opening degree of the gas proportional control valve 36 are adjusted with the current combustion stage, the output cannot be further increased by itself. Is affirmative (S210: YES). In this case, the controller 61 stores the maximum hot water temperature T _Nmax of the current combustion stage N (S230).

  Subsequently, the controller 61 determines whether or not the flag F2 is on (S240). As will be described in detail later, when the flag F2 is OFF in S240 (S240: NO), it can be determined that switching to lower the combustion stage by one stage is not performed in the output reduction control shown in FIG. Therefore, in this case, the controller 61 executes S260, S270, and S220 as in the first embodiment, performs the switching to increase the combustion stage by one, and ends the output increase control. .

On the other hand, when the flag F2 is ON in S240 (S240: YES), the controller 61 sets the maximum hot water temperature T _Nmax of the current combustion stage N and the minimum hot water temperature T _{(N + 1) min} of the combustion stage N + 1 that is one level higher. Based on the above, it is determined whether or not the set temperature is lower than (T _Nmax + T _{(N + 1) min} ) / 2 (S250).

The maximum hot water temperature T _Nmax of the current combustion stage N is a value stored in S230 described above. The minimum hot water temperature T _{(N + 1) min} of the combustion stage N + 1 that is one level above is a value stored in S330 of FIG. Therefore, (T _Nmax + T _{(N + 1) min} ) / 2 is an intermediate value between the maximum hot water temperature T _Nmax of the current combustion stage N and the minimum hot water temperature T _{(N + 1) min} of the combustion stage N + 1 one level higher. (Arithmetic mean value).

In S250, when the set temperature is (T _Nmax + T _{(N + 1) min} ) / 2 or more (S250: NO), the set temperatures are the maximum hot water temperature T _Nmax and the minimum hot water temperature T _{(N + 1) min} . It is possible to determine that the value is equal to the intermediate value or a value closer to the minimum hot water temperature T _{(N + 1) min} than the maximum hot water temperature T _Nmax . Therefore, in this case, the controller 61 executes S260, S270, and S220 as in the first embodiment, performs the switching to increase the combustion stage by one, and ends the output increase control. .

On the other hand, when the set temperature is smaller than (T _Nmax + T _{(N + 1) min} ) / 2 (S250: YES), the set temperature is the maximum tapping temperature T _Nmax than the minimum tapping temperature T _{(N + 1) min.} It can be determined that the value is close to. Therefore, in this case, the controller 61 does not execute S260, S270, and S220, and ends the output increase control without performing switching to increase the combustion stage by one stage.

  The difference between the output reduction control shown in FIG. 11 and the output reduction control shown in FIG. 7 is that processing steps S330, S350, and S360 that are not included in the output increase control shown in FIG. 7 are added. .

Hereinafter, the output reduction control in the present embodiment will be described focusing on the above differences. When the output reduction control is started, the controller 61 determines whether or not the minimum output of the current combustion stage has been reached as shown in FIG. 11 (S310). In S310, as in the first embodiment, if the rotation speed of the fan 21 and the opening of the gas proportional control valve 36 are adjusted with the current combustion stage, the output cannot be further reduced by itself. Is affirmative (S310: YES). In this case, the controller 61 stores the minimum hot water temperature T _Nmin of the current combustion stage N (S330).

  Subsequently, the controller 61 determines whether or not the flag F1 is on (S340). When the flag F1 is OFF in S340 (S340: NO), it can be determined that the switch to increase the combustion stage by one stage is not performed in the output increase control shown in FIG. Therefore, in this case, the controller 61 turns on the flag F2 (S360) and stores that the combustion stage is lowered by one stage. Then, the controller 61 changes the combustion stage from the N stage to the N-1 stage (S370).

  When S370 is finished, the process proceeds to S320. Thereby, the rotation speed of the fan 21 and the opening degree of the gas proportional control valve 36 are adjusted so that the output decreases in the combustion stage lowered by one stage in S370 (S320). When S320 is finished, the output increase control is finished.

On the other hand, when the flag F1 is ON in S340 (S340: YES), the controller 61 determines the minimum hot water temperature T _Nmin of the current combustion stage N and the maximum hot water temperature T _(N-1) of the combustion stage N-1 that is one lower. Based on _max , it is determined whether or not the set temperature is lower than (T _{(N-1) max} + T _Nmin ) / 2 (S350).

The minimum hot water temperature T _Nmin of the current combustion stage N is a value stored in S330 described above. The maximum hot water temperature T _{(N-1) max} of the next lower combustion stage N-1 is a value stored in S230 of FIG. Therefore, (T _{(N-1) max} + T _Nmin ) / 2 is the _difference between the minimum hot water temperature T _Nmin of the current combustion stage N and the maximum hot water temperature T _{(N-1) max} of the _next lower combustion stage N-1. It is an intermediate value (arithmetic mean value).

In S350, when the set temperature is less than (T _{(N-1) max} + T _Nmin ) / 2 (S350: NO), the set temperature is _higher than the minimum hot water temperature T _Nmin and the maximum hot water temperature T _{(N-1) max.} It can be determined that the value is close to. Therefore, in this case, the controller 61 executes the above-described S360, S370, and S320, and performs switching to lower the combustion stage by one, and then ends the output reduction control.

On the other hand, when the set temperature is (T _{(N-1) max} + T _Nmin ) / 2 or more (S350: YES), the set temperature is set to the minimum tapping temperature T _Nmin rather than the maximum tapping temperature T _{(N-1) max.} It can be determined that the values are close. Therefore, in this case, the controller 61 does not execute S360, S370, and S320, and ends the output reduction control without performing switching to lower the combustion stage by one stage.

  When the hot water supply process as described above is executed, the hot water heater 1 tries to operate at the point A shown in FIG. When the water heater 1 operates at the point B, the output becomes too small, so S120 in FIG. 9 (specifically, output increase control shown in FIG. 10) is executed. As a result, the water heater 1 tries to change the operating state from the A point to the C point side, but actually, the operating state of the water heater 1 changes from the B point to the D point side.

Thereafter, when the operating state of the water heater 1 reaches the point D, the water heater 1 recognizes that the operating state has reached the point C. Therefore, an affirmative determination is made in S210 of FIG. In this case, since the maximum hot water temperature T _Nmax of the current combustion stage N is stored in S230 and the flag F2 is initially off (S240: NO), the flag F1 is turned on in S260, and the combustion stage is increased by one stage in S270. It is done. Thereby, the water heater 1 shifts to a state of operating at the point E.

  When the operating state of the water heater 1 shifts to the point E, the water heater 1 enters a state where an output larger than the point A can be obtained. For this reason, the output becomes excessive, and in this state, the tapping temperature becomes higher than the set temperature, so S140 of FIG. 9 (specifically, output reduction control shown in FIG. 11) is executed. Thereby, the operating state of the water heater 1 changes from the E point to the F point side.

Thereafter, even when the operating state of the water heater 1 reaches the point F, the water heater 1 is still in a state where an output larger than the point A can be obtained. Therefore, an affirmative determination is made in S310 of FIG. In this case, the minimum hot water temperature T _Nmin of the current combustion stage N is stored in S330. Subsequently, at this time, since the flag F1 is turned on in the previously executed S260, the water heater 1 recognizes that the non-adjustable range as described above has occurred. In this case, in S350, the hot water heater 1 has a minimum hot water temperature T _Nmin of the current combustion stage N and a maximum hot water temperature T _{(N-1) max} of the combustion stage N-1 that is one lower. Judge whether it is close to the set temperature.

In S350, whether the temperature difference between the minimum hot water temperature T _Nmin of the current combustion stage N and the maximum hot water temperature T _{(N-1) max of the next} lower combustion stage N-1 is the same as the set temperature. When it is determined that the minimum hot water temperature T _Nmin of the combustion stage N is closer to the set temperature (S350: YES), the switching of the combustion stage (S370) is not performed. As a result, the water heater 1 continues to operate at point F. That is, when the water heater 1 recognizes that an unadjustable range has occurred, in S350, the minimum hot water temperature T _Nmin of the current combustion stage N and the maximum hot water temperature T ₍ in the _{N-1) max,} combustion stage under one N-1 of the maximum hot water temperature T _(N-1) as long as the determination of the direction of _max is close to the set temperature is not performed, a state operating at point F In this way, the occurrence of hunting in the switching of the combustion stage is suppressed.

On the other hand, the flag F2 is turned on in S360 only when it is determined in S350 that the maximum hot water temperature T _{(N-1) max} of the next lower combustion stage N-1 is closer to the set temperature. In S370, the combustion stage is lowered by one stage. Thereby, the water heater 1 shifts to a state of operating at the point G.

  When the water heater 1 is operated at the point G, the output becomes too small, so S120 in FIG. 9 (specifically, output increase control shown in FIG. 10) is executed. Thereby, the operation state of the water heater 1 changes from the G point to the D point side.

Thereafter, when the operating state of the water heater 1 reaches the point D, the water heater 1 recognizes that the operating state has reached the point C. Therefore, an affirmative determination is made in S210 of FIG. In this case, the maximum hot water temperature T _Nmax of the current combustion stage N is stored in S230, and the flag F2 is turned on this time (S240: YES). The water heater 1 recognizes that the non-adjustable range as described above occurs. In this case, the water heater 1 determines in S250 which temperature is the set temperature between the maximum hot water temperature T _Nmax of the current combustion stage N and the minimum hot water temperature T _{(N + 1) min} of the combustion stage N + 1 that is one level higher. It is judged whether it is near.

In S250, only the same determination as S350 performed previously is performed, so this time, it is determined that the maximum hot water temperature T _Nmax of the current combustion stage N is closer to the set temperature (S250: YES). Therefore, the combustion stage switching (S370) is not performed. As a result, the water heater 1 continues to operate at the point D, thereby suppressing the occurrence of hunting in the switching of the combustion stage.

  As described above, in the second embodiment, when it is recognized that the non-adjustable range as described above is generated, the combustion temperature on both sides of the non-adjustable range is made closer to the set temperature. After switching to a possible combustion stage, the operating state is continued in that combustion stage. In this respect, the operation state is continued at the minimum output of the combustion stage one level higher without judging which combustion stage is close to the set temperature among the combustion stages on both sides of the non-adjustable range. This is different from the first embodiment configured as described above.

  Therefore, in the case of the second embodiment, it is more beneficial than the first embodiment in that the temperature can be made closer to the set temperature. On the other hand, in the case of the first embodiment, since the operation state is continued in the upper combustion stage, the rotational speed of the fan 21 and the opening degree of the gas proportional control valve 36 can be suppressed to be low. Generally, the operation state of the water heater 1 is more stable when the rotational speed of the fan 21 and the opening degree of the gas proportional control valve 36 are kept low. From this viewpoint, the configuration of the first embodiment is also beneficial. is there. Therefore, which of the configurations of the first embodiment and the second embodiment is adopted may be arbitrarily selected in consideration of which advantage is emphasized.

  In the second embodiment described above, the controller 61 functions as a feedback control unit referred to in this specification by executing the feedback temperature control shown in FIG. Further, the controller 61 executes S210, S230, S240, S250, and S260 in FIG. 10 and S310, S330, S340, S350, and S360 in FIG. 11 to function as a determination unit in this specification. Further, the controller 61 makes an affirmative determination in S210 of FIG. 10 to skip S260, S270, and S220, and performs an affirmative determination in S310 of FIG. 11 to skip S360, S370, and S320. It functions as a feedback control prohibition unit referred to in this specification.

(3) Other Embodiments While the hot water heater has been described with reference to the exemplary embodiment, the above-described embodiment is merely illustrated as one aspect of the present invention. That is, the present invention is not limited to the exemplary embodiments described above, and can be implemented in various forms without departing from the technical idea of the present invention.

  For example, in the above embodiment, the operation state is continued at the minimum output of the upper combustion stage among the combustion stages on both sides of the non-adjustable range (first embodiment), and closer to the set temperature. Although the example (2nd embodiment) which continues an operation state with the combustion stage which can be shown was shown, aspects other than these can also be considered. For example, the operation state may be continued at the maximum output of the lower combustion stage among the combustion stages on both sides of the non-adjustable range.

(4) Supplement It can be understood from the exemplary embodiments described above that the water heater described in this specification may further include the following configurations.

  First, in the water heater described in the present specification, the determination unit performs control from one of the i-th combustion stage and the i + 1th combustion stage to the other combustion stage during the control by the feedback control unit. It may be determined that the non-adjustable range has occurred when switching from the other combustion stage to the one combustion stage becomes necessary after switching to.

According to the water heater configured as described above, when the non-adjustable range is generated, it is possible to appropriately determine that the non-adjustable range is generated by the above-described method.
Further, in the water heater described in the present specification, when the determination unit determines that the non-adjustable range is generated, the feedback control prohibition unit does not switch from the other combustion stage to the one combustion stage. Thus, the switching valve, the proportional control valve, and the actual combustion output are fixed at either the upper limit value of the combustion output in the i-th combustion stage or the lower limit value of the combustion output in the i + 1-th combustion stage. The blower may be controlled.

  According to the water heater configured in this way, when the combustion output is fixed at an output smaller than the upper limit value of the combustion output in the i-th combustion stage, or the lower limit of the combustion output in the i + 1-th combustion stage Compared to the case where the output is fixed at a value larger than the value, a hot water temperature closer to the set temperature can be obtained.

  Further, in the water heater described in the present specification, when the determination unit determines that the non-adjustable range has occurred, the feedback control prohibition unit determines that the actual combustion output is the combustion output in the i + 1th combustion stage. The switching valve, the proportional control valve, and the blower may be controlled so as to be fixed at the lower limit value.

  According to the water heater configured as described above, the combustion output is fixed at the lower limit value of the combustion output in the (i + 1) th combustion stage. Therefore, compared with the case where the combustion output is fixed at the upper limit value of the combustion output in the i-th combustion stage, the rotational speed of the blower and the opening degree of the proportional control valve can be suppressed to be lower. Thereby, the operation state of the water heater can be changed to a more stable operation state.

  Further, in the water heater described in the present specification, when it is determined by the determination unit that the non-adjustable range has occurred, the feedback control prohibition unit determines the upper limit value of the combustion output in the i-th combustion stage and the (i + 1) th The lower limit value of the combustion output in the combustion stage of the engine is determined as to which value is close to the required combustion output, and the switching valve and proportional control are performed so that the actual combustion output is fixed at a value close to the required combustion output. You may control a valve and an air blower.

  According to the water heater configured as described above, when the required combustion output is close to the upper limit value of the i-th combustion stage and when the required combustion output is close to the lower limit value of the i + 1-th combustion stage, in any case In this case, the hot water temperature closer to the set temperature can be obtained.

  DESCRIPTION OF SYMBOLS 1 ... Hot water heater, 2 ... Hot water tap, 11 ... Combustion chamber, 12A, 12B, 12C ... Burner, 13 ... Primary heat exchanger, 14 ... Secondary heat exchanger, 15 ... Electrode, 16 ... Igniter, 17 ... Frame rod , 18 ... drain drain pipe, 19 ... neutralizer, 20 ... fan motor, 21 ... fan, 22 ... exhaust top, 23 ... overheating prevention device, 31 ... gas supply pipe, 32 ... main pipe, 33A, 33B, 33C ... Branch pipe, 34A, 34B, 34C ... Nozzle, 35 ... Original solenoid valve, 36 ... Gas proportional control valve, 37A, 37B, 37C ... Switching solenoid valve, 41 ... Water supply pipe, 43 ... Hot water pipe, 45 ... Bypass pipe, 51 ... Strainer, 52 ... Water quantity sensor, 53 ... Water quantity control motor, 54 ... Thermistor for detecting incoming water temperature, 55 ... Thermistor for preventing freezing, 56 ... Thermistor for detecting hot water temperature at the inner trunk outlet, 57 ... Thermistor for detecting hot water temperature , 58 ... pressure relief valve with drain tap, 59 ... bypass control motor, 61 ... controller, 62 ... remote control.

Claims (5)

With multiple burners,
A proportional control valve capable of adjusting the amount of fuel supplied to the burner;
A blower capable of adjusting an air supply amount to the burner;
A switching valve capable of switching whether to supply fuel to each of the plurality of burner parts;
By switching between which of the plurality of burner sections the fuel is supplied by controlling the switching valve, it is possible to switch between a plurality of combustion stages having different lower and upper limit values of combustion output, and A control unit capable of adjusting the combustion output within a range from a lower limit value to an upper limit value of the combustion output in each combustion stage by controlling the proportional control valve and the blower, and
The controller is
Based on the set temperature arbitrarily set and the actual tapping temperature, the required combustion output necessary for tapping at the set temperature is calculated, and the changeover valve, the proportional control valve so as to obtain the necessary combustion output. And a feedback control unit for controlling the blower,
Of the combustion stages from the 1st to the nth (where n is an integer of 2 or more) in which the combustion output increases in order, the i-th (where i is an integer satisfying 1 ≦ i <n). Between the upper limit value of the combustion output in the stage and the lower limit value of the combustion output in the (i + 1) th combustion stage, there is an unadjustable range that is a numerical range that exceeds the upper limit value and falls below the lower limit value. A determination unit capable of determining
When the necessary combustion output calculated by the feedback control unit is within the non-adjustable range determined by the determination unit, the actual combustion output is an upper limit value of the combustion output in the i-th combustion stage, Or a feedback control prohibiting unit that controls the switching valve, the proportional control valve, and the blower so as to be fixed at any one of the lower limit values of the combustion output in the (i + 1) th combustion stage. The water heater according to claim 1,
In the control by the feedback control unit, the determination unit switches from any one of the combustion stages to the other combustion stage among the i-th combustion stage and the i + 1-th combustion stage. When it is necessary to switch from one combustion stage to the other combustion stage, it is determined that the non-adjustable range has occurred. The water heater according to claim 2,
When the determination unit determines that the non-adjustable range has occurred, the feedback control prohibition unit does not switch from the other combustion stage to the one combustion stage, thereby causing an actual combustion output. Is fixed at either the upper limit value of the combustion output in the i-th combustion stage or the lower limit value of the combustion output in the i + 1-th combustion stage, the switching valve, the proportional control valve, and the blower. Water heater to control. A water heater according to claim 2 or claim 3, wherein
When the determination unit determines that the non-adjustable range has occurred, the feedback control prohibition unit causes the actual combustion output to be fixed at the lower limit value of the combustion output in the i + 1th combustion stage. The water heater that controls the switching valve, the proportional control valve, and the blower. The water heater according to claim 2,
When the determination unit determines that the non-adjustable range has occurred, the feedback control prohibition unit determines the upper limit value of the combustion output in the i th combustion stage and the combustion output in the i + 1 th combustion stage. It is determined which of the lower limit values is close to the required combustion output, and the switching valve, the proportional control valve, and the proportional control valve are set so that the actual combustion output is fixed at a value close to the required combustion output. A water heater that controls the blower.

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